\section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
\begin{code}
-module WorkWrap ( workersAndWrappers, getWorkerIdAndCons ) where
+module WorkWrap ( wwTopBinds, mkWrapper ) where
#include "HsVersions.h"
import CoreSyn
-import CoreUnfold ( Unfolding, certainlySmallEnoughToInline, calcUnfoldingGuidance )
-import CmdLineOpts ( opt_UnfoldingCreationThreshold )
-
-import CoreUtils ( coreExprType )
-import Const ( Con(..) )
-import DataCon ( DataCon )
-import MkId ( mkWorkerId )
-import Id ( Id, getIdStrictness,
- setIdStrictness, setInlinePragma, idWantsToBeINLINEd,
+import CoreUnfold ( certainlyWillInline )
+import CoreLint ( showPass, endPass )
+import CoreUtils ( exprType, exprIsValue )
+import Id ( Id, idType, isOneShotLambda,
+ setIdNewStrictness, mkWorkerId,
+ setIdWorkerInfo, setInlinePragma,
+ idInfo )
+import Type ( Type )
+import IdInfo ( WorkerInfo(..), arityInfo,
+ newDemandInfo, newStrictnessInfo, unfoldingInfo, inlinePragInfo
)
-import VarSet
-import Type ( splitAlgTyConApp_maybe )
-import IdInfo ( mkStrictnessInfo, StrictnessInfo(..),
- InlinePragInfo(..) )
-import SaLib
-import UniqSupply ( UniqSupply, initUs, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
-import UniqSet
+import NewDemand ( Demand(..), StrictSig(..), DmdType(..), DmdResult(..),
+ Demands(..), mkTopDmdType, isBotRes, returnsCPR, topSig, isAbsent
+ )
+import UniqSupply ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
+import BasicTypes ( RecFlag(..), isNonRec, Activation(..) )
+import VarEnv ( isEmptyVarEnv )
+import Maybes ( orElse )
+import CmdLineOpts
import WwLib
+import Util ( lengthIs )
import Outputable
\end{code}
-We take Core bindings whose binders have their strictness attached (by
-the front-end of the strictness analyser), and we return some
-``plain'' bindings which have been worker/wrapper-ified, meaning:
+We take Core bindings whose binders have:
+
\begin{enumerate}
-\item
-Functions have been split into workers and wrappers where appropriate;
-\item
-Binders' @IdInfos@ have been updated to reflect the existence
-of these workers/wrappers (this is where we get STRICTNESS pragma
+
+\item Strictness attached (by the front-end of the strictness
+analyser), and / or
+
+\item Constructed Product Result information attached by the CPR
+analysis pass.
+
+\end{enumerate}
+
+and we return some ``plain'' bindings which have been
+worker/wrapper-ified, meaning:
+
+\begin{enumerate}
+
+\item Functions have been split into workers and wrappers where
+appropriate. If a function has both strictness and CPR properties
+then only one worker/wrapper doing both transformations is produced;
+
+\item Binders' @IdInfos@ have been updated to reflect the existence of
+these workers/wrappers (this is where we get STRICTNESS and CPR pragma
info for exported values).
\end{enumerate}
\begin{code}
+
+wwTopBinds :: DynFlags
+ -> UniqSupply
+ -> [CoreBind]
+ -> IO [CoreBind]
+
+wwTopBinds dflags us binds
+ = do {
+ showPass dflags "Worker Wrapper binds";
+
+ -- Create worker/wrappers, and mark binders with their
+ -- "strictness info" [which encodes their worker/wrapper-ness]
+ let { binds' = workersAndWrappers us binds };
+
+ endPass dflags "Worker Wrapper binds"
+ Opt_D_dump_worker_wrapper binds'
+ }
+\end{code}
+
+
+\begin{code}
workersAndWrappers :: UniqSupply -> [CoreBind] -> [CoreBind]
workersAndWrappers us top_binds
- = initUs us $
- mapUs (wwBind True{-top-level-}) top_binds `thenUs` \ top_binds2 ->
- let
- top_binds3 = map make_top_binding top_binds2
- in
- returnUs (concat top_binds3)
- where
- make_top_binding :: WwBinding -> [CoreBind]
-
- make_top_binding (WwLet binds) = binds
+ = initUs_ us $
+ mapUs wwBind top_binds `thenUs` \ top_binds' ->
+ returnUs (concat top_binds')
\end{code}
%************************************************************************
turn. Non-recursive case first, then recursive...
\begin{code}
-wwBind :: Bool -- True <=> top-level binding
- -> CoreBind
- -> UniqSM WwBinding -- returns a WwBinding intermediate form;
+wwBind :: CoreBind
+ -> UniqSM [CoreBind] -- returns a WwBinding intermediate form;
-- the caller will convert to Expr/Binding,
-- as appropriate.
-wwBind top_level (NonRec binder rhs)
- = wwExpr rhs `thenUs` \ new_rhs ->
- tryWW True {- non-recursive -} binder new_rhs `thenUs` \ new_pairs ->
- returnUs (WwLet [NonRec b e | (b,e) <- new_pairs])
+wwBind (NonRec binder rhs)
+ = wwExpr rhs `thenUs` \ new_rhs ->
+ tryWW NonRecursive binder new_rhs `thenUs` \ new_pairs ->
+ returnUs [NonRec b e | (b,e) <- new_pairs]
-- Generated bindings must be non-recursive
-- because the original binding was.
-------------------------------
-
-wwBind top_level (Rec pairs)
+wwBind (Rec pairs)
= mapUs do_one pairs `thenUs` \ new_pairs ->
- returnUs (WwLet [Rec (concat new_pairs)])
+ returnUs [Rec (concat new_pairs)]
where
do_one (binder, rhs) = wwExpr rhs `thenUs` \ new_rhs ->
- tryWW False {- recursive -} binder new_rhs
+ tryWW Recursive binder new_rhs
\end{code}
@wwExpr@ basically just walks the tree, looking for appropriate
annotations that can be used. Remember it is @wwBind@ that does the
matching by looking for strict arguments of the correct type.
@wwExpr@ is a version that just returns the ``Plain'' Tree.
-???????????????? ToDo
\begin{code}
wwExpr :: CoreExpr -> UniqSM CoreExpr
wwExpr e@(Type _) = returnUs e
wwExpr e@(Var _) = returnUs e
-
-wwExpr e@(Con con args)
- = mapUs wwExpr args `thenUs` \ args' ->
- returnUs (Con con args')
+wwExpr e@(Lit _) = returnUs e
wwExpr (Lam binder expr)
= wwExpr expr `thenUs` \ new_expr ->
returnUs (Note note new_expr)
wwExpr (Let bind expr)
- = wwBind False{-not top-level-} bind `thenUs` \ intermediate_bind ->
- wwExpr expr `thenUs` \ new_expr ->
- returnUs (mash_ww_bind intermediate_bind new_expr)
- where
- mash_ww_bind (WwLet binds) body = mkLets binds body
- mash_ww_bind (WwCase case_fn) body = case_fn body
+ = wwBind bind `thenUs` \ intermediate_bind ->
+ wwExpr expr `thenUs` \ new_expr ->
+ returnUs (mkLets intermediate_bind new_expr)
wwExpr (Case expr binder alts)
= wwExpr expr `thenUs` \ new_expr ->
The only reason this is monadised is for the unique supply.
\begin{code}
-tryWW :: Bool -- True <=> a non-recursive binding
+tryWW :: RecFlag
-> Id -- The fn binder
-> CoreExpr -- The bound rhs; its innards
-- are already ww'd
-- the orig "wrapper" lives on);
-- if two, then a worker and a
-- wrapper.
-tryWW non_rec fn_id rhs
- | idWantsToBeINLINEd fn_id
- || (non_rec && -- Don't split if its non-recursive and small
- certainlySmallEnoughToInline fn_id unfold_guidance
- )
- -- No point in worker/wrappering something that is going to be
- -- INLINEd wholesale anyway. If the strictness analyser is run
- -- twice, this test also prevents wrappers (which are INLINEd)
- -- from being re-done.
-
- || not has_strictness_info
- || not (worthSplitting revised_wrap_args_info)
- = returnUs [ (fn_id, rhs) ]
-
- | otherwise -- Do w/w split
- = let
- (tyvars, wrap_args, body) = collectTyAndValBinders rhs
- in
- mkWwBodies tyvars wrap_args
- (coreExprType body)
- revised_wrap_args_info `thenUs` \ (wrap_fn, work_fn, work_demands) ->
- getUniqueUs `thenUs` \ work_uniq ->
+tryWW is_rec fn_id rhs
+ | isNonRec is_rec && certainlyWillInline unfolding
+ -- No point in worker/wrappering a function that is going to be
+ -- INLINEd wholesale anyway. If the strictness analyser is run
+ -- twice, this test also prevents wrappers (which are INLINEd)
+ -- from being re-done.
+ --
+ -- It's very important to refrain from w/w-ing an INLINE function
+ -- If we do so by mistake we transform
+ -- f = __inline (\x -> E)
+ -- into
+ -- f = __inline (\x -> case x of (a,b) -> fw E)
+ -- fw = \ab -> (__inline (\x -> E)) (a,b)
+ -- and the original __inline now vanishes, so E is no longer
+ -- inside its __inline wrapper. Death! Disaster!
+ = returnUs [ (fn_id', rhs) ]
+
+ | is_thunk && worthSplittingThunk fn_dmd res_info
+ = ASSERT( isNonRec is_rec ) -- The thunk must be non-recursive
+ splitThunk fn_id' rhs
+
+ | is_fun && worthSplittingFun wrap_dmds res_info
+ = splitFun fn_id' fn_info wrap_dmds res_info inline_prag rhs
+
+ | otherwise
+ = returnUs [ (fn_id', rhs) ]
+
+ where
+ fn_info = idInfo fn_id
+ fn_dmd = newDemandInfo fn_info
+ unfolding = unfoldingInfo fn_info
+ inline_prag = inlinePragInfo fn_info
+ maybe_sig = newStrictnessInfo fn_info
+
+ -- In practice it always will have a strictness
+ -- signature, even if it's a uninformative one
+ strict_sig = newStrictnessInfo fn_info `orElse` topSig
+ StrictSig (DmdType env wrap_dmds res_info) = strict_sig
+
+ -- fn_id' has the DmdEnv zapped.
+ -- (a) it is never used again
+ -- (b) it wastes space
+ -- (c) it becomes incorrect as things are cloned, because
+ -- we don't push the substitution into it
+ fn_id' | isEmptyVarEnv env = fn_id
+ | otherwise = fn_id `setIdNewStrictness`
+ StrictSig (mkTopDmdType wrap_dmds res_info)
+
+ is_fun = not (null wrap_dmds)
+ is_thunk = not is_fun && not (exprIsValue rhs)
+
+---------------------
+splitFun fn_id fn_info wrap_dmds res_info inline_prag rhs
+ = WARN( not (wrap_dmds `lengthIs` arity), ppr fn_id <+> (ppr arity $$ ppr wrap_dmds $$ ppr res_info) )
+ -- The arity should match the signature
+ mkWwBodies fun_ty wrap_dmds res_info one_shots `thenUs` \ (work_demands, wrap_fn, work_fn) ->
+ getUniqueUs `thenUs` \ work_uniq ->
let
- work_rhs = work_fn body
- work_id = mkWorkerId work_uniq fn_id (coreExprType work_rhs) `setIdStrictness`
- mkStrictnessInfo work_demands False
+ work_rhs = work_fn rhs
+ work_id = mkWorkerId work_uniq fn_id (exprType work_rhs)
+ `setInlinePragma` inline_prag
+ `setIdNewStrictness` StrictSig (mkTopDmdType work_demands work_res_info)
+ -- Even though we may not be at top level,
+ -- it's ok to give it an empty DmdEnv
wrap_rhs = wrap_fn work_id
- wrap_id = fn_id `setIdStrictness` mkStrictnessInfo revised_wrap_args_info True
- `setInlinePragma` IWantToBeINLINEd
- -- Add info to the wrapper:
- -- (a) we want to inline it everywhere
- -- (b) we want to pin on its revised stricteness info
- -- (c) we pin on its worker id and the list of constructors mentioned in the wrapper
+ wrap_id = fn_id `setIdWorkerInfo` HasWorker work_id arity
+ `setInlinePragma` AlwaysActive -- Zap any inline pragma;
+ -- Put it on the worker instead
in
returnUs ([(work_id, work_rhs), (wrap_id, wrap_rhs)])
-- Worker first, because wrapper mentions it
+ -- mkWwBodies has already built a wrap_rhs with an INLINE pragma wrapped around it
where
- strictness_info = getIdStrictness fn_id
- has_strictness_info = case strictness_info of
- StrictnessInfo _ _ -> True
- other -> False
-
- wrap_args_info = case strictness_info of
- StrictnessInfo args_info _ -> args_info
- revised_wrap_args_info = setUnpackStrategy wrap_args_info
-
- unfold_guidance = calcUnfoldingGuidance opt_UnfoldingCreationThreshold rhs
-
--- This rather (nay! extremely!) crude function looks at a wrapper function, and
--- snaffles out (a) the worker Id and (b) constructors needed to
--- make the wrapper.
--- These are needed when we write an interface file.
-getWorkerIdAndCons :: Id -> CoreExpr -> (Id, UniqSet DataCon)
-getWorkerIdAndCons wrap_id wrapper_fn
- = (get_work_id wrapper_fn, get_cons wrapper_fn)
+ fun_ty = idType fn_id
+
+ arity = arityInfo fn_info -- The arity is set by the simplifier using exprEtaExpandArity
+ -- So it may be more than the number of top-level-visible lambdas
+
+ work_res_info | isBotRes res_info = BotRes -- Cpr stuff done by wrapper
+ | otherwise = TopRes
+
+ one_shots = get_one_shots rhs
+
+-- If the original function has one-shot arguments, it is important to
+-- make the wrapper and worker have corresponding one-shot arguments too.
+-- Otherwise we spuriously float stuff out of case-expression join points,
+-- which is very annoying.
+get_one_shots (Lam b e)
+ | isId b = isOneShotLambda b : get_one_shots e
+ | otherwise = get_one_shots e
+get_one_shots (Note _ e) = get_one_shots e
+get_one_shots other = noOneShotInfo
+\end{code}
+
+Thunk splitting
+~~~~~~~~~~~~~~~
+Suppose x is used strictly (never mind whether it has the CPR
+property).
+
+ let
+ x* = x-rhs
+ in body
+
+splitThunk transforms like this:
+
+ let
+ x* = case x-rhs of { I# a -> I# a }
+ in body
+
+Now simplifier will transform to
+
+ case x-rhs of
+ I# a -> let x* = I# b
+ in body
+
+which is what we want. Now suppose x-rhs is itself a case:
+
+ x-rhs = case e of { T -> I# a; F -> I# b }
+
+The join point will abstract over a, rather than over (which is
+what would have happened before) which is fine.
+
+Notice that x certainly has the CPR property now!
+
+In fact, splitThunk uses the function argument w/w splitting
+function, so that if x's demand is deeper (say U(U(L,L),L))
+then the splitting will go deeper too.
+
+\begin{code}
+-- splitThunk converts the *non-recursive* binding
+-- x = e
+-- into
+-- x = let x = e
+-- in case x of
+-- I# y -> let x = I# y in x }
+-- See comments above. Is it not beautifully short?
+
+splitThunk fn_id rhs
+ = mkWWstr [fn_id] `thenUs` \ (_, wrap_fn, work_fn) ->
+ returnUs [ (fn_id, Let (NonRec fn_id rhs) (wrap_fn (work_fn (Var fn_id)))) ]
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Functions over Demands}
+%* *
+%************************************************************************
+
+\begin{code}
+worthSplittingFun :: [Demand] -> DmdResult -> Bool
+ -- True <=> the wrapper would not be an identity function
+worthSplittingFun ds res
+ = any worth_it ds || returnsCPR res
+ -- worthSplitting returns False for an empty list of demands,
+ -- and hence do_strict_ww is False if arity is zero and there is no CPR
+
+ -- We used not to split if the result is bottom.
+ -- [Justification: there's no efficiency to be gained.]
+ -- But it's sometimes bad not to make a wrapper. Consider
+ -- fw = \x# -> let x = I# x# in case e of
+ -- p1 -> error_fn x
+ -- p2 -> error_fn x
+ -- p3 -> the real stuff
+ -- The re-boxing code won't go away unless error_fn gets a wrapper too.
+ -- [We don't do reboxing now, but in general it's better to pass
+ -- an unboxed thing to f, and have it reboxed in the error cases....]
where
- get_work_id (Lam _ body) = get_work_id body
- get_work_id (Case _ _ [(_,_,rhs)]) = get_work_id rhs
- get_work_id (Note _ body) = get_work_id body
- get_work_id (Let _ body) = get_work_id body
- get_work_id (App fn _) = get_work_id fn
- get_work_id (Var work_id) = work_id
- get_work_id other = pprPanic "getWorkerIdAndCons" (ppr wrap_id)
-
-
- get_cons (Lam _ body) = get_cons body
- get_cons (Let (NonRec _ rhs) body) = get_cons rhs `unionUniqSets` get_cons body
-
- get_cons (Case e _ [(DataCon dc,_,rhs)]) = (get_cons e `unionUniqSets` get_cons rhs)
- `addOneToUniqSet` dc
-
- -- Coercions don't mention the construtor now,
- -- but we must still put the constructor in the interface
- -- file so that the RHS of the newtype decl is imported
- get_cons (Note (Coerce to_ty from_ty) body)
- = get_cons body `addOneToUniqSet` con
- where
- con = case splitAlgTyConApp_maybe from_ty of
- Just (_, _, [con]) -> con
- other -> pprPanic "getWorkerIdAndCons" (ppr to_ty)
-
- get_cons other = emptyUniqSet
+ worth_it Abs = True -- Absent arg
+ worth_it (Eval (Prod ds)) = True -- Product arg to evaluate
+ worth_it other = False
+
+worthSplittingThunk :: Demand -- Demand on the thunk
+ -> DmdResult -- CPR info for the thunk
+ -> Bool
+worthSplittingThunk dmd res
+ = worth_it dmd || returnsCPR res
+ where
+ -- Split if the thing is unpacked
+ worth_it (Eval (Prod ds)) = not (all isAbsent ds)
+ worth_it other = False
+\end{code}
+
+
+
+%************************************************************************
+%* *
+\subsection{The worker wrapper core}
+%* *
+%************************************************************************
+
+@mkWrapper@ is called when importing a function. We have the type of
+the function and the name of its worker, and we want to make its body (the wrapper).
+
+\begin{code}
+mkWrapper :: Type -- Wrapper type
+ -> StrictSig -- Wrapper strictness info
+ -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
+
+mkWrapper fun_ty (StrictSig (DmdType _ demands res_info))
+ = mkWwBodies fun_ty demands res_info noOneShotInfo `thenUs` \ (_, wrap_fn, _) ->
+ returnUs wrap_fn
+
+noOneShotInfo = repeat False
\end{code}
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